Proper operation of a telecommunication network requires time and/or frequency synchronization between various entities therein. Synchronization can be achieved, for example, by exchange timing information (time-transfer) across the network. A particular protocol for exchanging timing information over a packet-compatible network is the IEEE 1588 Precision Time Protocol (PTP) usable for frequency and phase synchronization.
For purpose of illustration only, the following description is provided for PTP-based synchronization. Those skilled in the art will readily appreciate that the teachings of the presently disclosed subject matter are, likewise, applicable to other time-transfer protocols and/or procedures that are usable for the exchange of time-related information in a packet-compatible network.
Through exchange of PTP packets, which include timestamps carried inside, PTP enables synchronization between a master clock node, which has access to an accurate time source (e.g. Global Positioning System) and slave clock nodes having less accurate clocks. Timestamps are usable for frequency and phase recovery between the clocks. For example, timestamps can be used to measure the roundtrip delay between the master node and a slave node. Knowledge of this path delay may then be used to synchronize a clock at the slave node with a master clock at the master node, based on a synchronization or timing reference received by the slave node from the master node. According to PTP, synchronization at the slave clock can be achieved without requiring changes in one or more intermediate nodes. In addition, boundary clocks and/or transparent clocks may be used, for example, to reduce effects of propagation delay variations and/or other delays.
Problems of synchronization of telecommunication networks by exchanging specialized messages between master and slave clocks have been recognized in the conventional art and various techniques have been developed to provide solutions, for example:
US Patent Application No. 2015/0171980 discloses a method for synchronizing distributed clocks by the Precision Time Protocol. The method includes sending a Sync message from a first peer-to-peer transparent clock to a second peer-to-peer transparent clock, estimating the path delay of the transmission path travelled by the synchronization message from the first to the second peer-to-peer transparent clocks, and taking this path delay into account for updating the time information carried by a synchronization message. The estimating includes creating a list of the network addresses of the network interfaces traversed by the synchronization message; ordering the first list into the order in which the network interfaces have been traversed by the Sync message; creating a second list by reversing the order of the first list; communicating the second list to the second peer-to-peer transparent clock; and using the mechanism available at the transport protocol level, to constrain the respective paths of Pdelay_Req and Pdelay_Resp messages so that their respective paths map to the second and first ordered lists of traversed interfaces.
US Patent Application No. 2015/0113174 discloses an intelligent supervisor located at a management node in the PTP network and configured to determine the PTP roles and configuration of the client nodes. The intelligent supervisor communicates with intelligent supervisor agents located at client nodes in the PTP network. The supervisor agents at the client nodes feed back information, such as the PTP properties of the client nodes, to the supervisor. The supervisor analyses the data to determine the roles and appropriate configuration for the client nodes.
US Patent Application No. 2013/0215889 discloses a data network node implementing a time-transfer protocol (e.g. Precision Time Protocol), wherein low-touch PTP packet processing functions moved from a PTP processing unit into an efficient network processor. An example network node includes a time-transfer protocol processing unit that generates negotiation messages and management messages for a time-transfer protocol and forwards said negotiation and management messages to one or more clients. The network node also includes a separate network processor unit, which is adapted to: receive a configuration message from the time-transfer protocol processing unit, the configuration message comprising stream configuration data for a first type of repetitive time-transfer message; generate a plurality of time-transfer messages according to the first type of repetitive time-transfer message, using the stream configuration data; and forward said plurality of time-transfer messages to the one or more remote network nodes, via the one or more line ports.
US Patent Application No. 2011/0261917 discloses a slave node in a packet network which achieves time synchronization with a master node by implementing a packet-layer synchronization procedure, such as the IEEE1588 precision timing protocol (PTP), to set the slave's local time based on the master's time. The slave's local time is then maintained by implementing a physical-layer synchronization procedure, such as synchronous Ethernet, without relying on the packet-layer synchronization procedure. The packet-layer synchronization procedure may be selectively employed to adjust the slave's local time (if needed) after significant periods of time (e.g., substantially greater than one second). Both the packet-layer synchronization procedure and the physical-layer synchronization procedure are traceable to a common reference timescale (e.g., UTC). Depending on the implementation, the packet-layer synchronization procedure can be, but does not have to be, terminated when not being employed to adjust the slave's local time.
The references cited above teach background information that may be applicable to the presently disclosed subject matter. Therefore the full contents of these publications are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.